Finely chop the onions, celery, parsley, and cilantro. Place the chickpeas in a bowl of lukewarm water to soften while you prepare the vegetables.
Heat the oil in a large heavy-bottomed pot over low heat. Add the onions and celery, cover, and cook until softened, about 8 minutes. Stir in the garlic, turmeric, paprika, cumin, black pepper, and salt. Cover and cook 2 to 3 minutes more, until fragrant.
Add the chickpeas, lentils, tomatoes, parsley, and cilantro. Cover and cook for 5 minutes so the flavors begin to blend. Pour in 8 to 10 cups/2 to 2.5 liters boiling water. Return to a gentle simmer, cover, and cook for 45 minutes, stirring occasionally.
In a small bowl, whisk the flour with a few tablespoons of cold water until smooth, with no lumps. Stir the mixture into the soup along with the noodles. Simmer uncovered for 25 minutes more, until the noodles are tender and the soup has lightly thickened.
Serve hot.